Related art inkjet image forming apparatuses such as inkjet printers, etc., are known that include a head which turns a recording liquid such as ink, etc., from multiple micro nozzles into liquid droplets to eject the droplets to perform inkjet recording by a movable actuator scheme represented by a piezoelectric scheme or a heating film boiling scheme represented by a thermal scheme, etc. (see Patent Documents 1 to 3, for example).
In an inkjet scheme, with the feature that the recording liquid is directly ejected from the head onto recording material such as recording paper, etc., the head and the recording material approach each other, so that paper dust, dust, etc., that are adhered to the recording material are likely to adhere to a nozzle. If the paper dust, etc., adhere to the nozzle, a flying direction of liquid droplets which are ejected from the nozzle is disturbed, or the nozzle is clogged, so that image quality and reliability decrease. As a measure for avoiding such a problem, it is common to give priority to stability of ejecting from the nozzle and use the recording liquid with a low viscosity. However, with the recording liquid with the low viscosity, a blur is likely to occur when it impacts onto the recording material.
Thus, image forming apparatuses are being proposed that include an intermediate transfer body which carries the recording liquid ejected from the head, wherein an image is formed onto the intermediate transfer body, after which the formed image is transferred onto the recording material (see Patent Documents 1 to 3).
More specifically, a technique is being proposed that uses a head which ejects conductive ink including water; an intermediate transfer body having a conductive surface onto which the ink which is ejected by the head is provided; a potential applying unit which applies a potential which can electrolyze water within a liquid column of ink which temporarily bridges between the head and the intermediate transfer body; and a transfer unit which transfers an ink image carried on the intermediate transfer body onto the recording material, wherein the potential is applied by the potential applying unit between an electrode within the head and a surface of the intermediate transfer body, and a pH change caused by electrolysis of the water within the liquid column of ink is used to increase viscosity of the ink to seek increasing preventability of an ink blur and stability of ejecting the ink from the nozzle (see Patent Documents 1 to 3, for example).
However, it has been recognized by a validation of the inventors that a problem may arise that, if such a technique is used, the pH of the ink within the head ends up changing towards a direction of preventing an increase in the viscosity as the electrode for electrolyzing the water within the ink is provided within the head, so that ejecting of the ink with the pH changed in such a manner causes the increase in the viscosity of the ink on the intermediate transfer body to be inhibited.
With respect to the above-described problem, it is implied that if the electrode is a nozzle plate which is provided in the head and with which the ink is in contact, when a contact area of the nozzle plate to the ink is compared with an area of a liquid column which is in contact with an intermediate transfer body surface, in case the former area is sufficiently larger than the latter area, electrolysis at an interface between the nozzle plate and the ink does not occur, so that the increase in the viscosity of the ink is inhibited. Moreover, if such an implication is correct, a technique which increases the above-described contact area (see Patent documents 2 and 3, for example) leads to a decreased likelihood of such a problem occurring.
However, according to a more detailed validation by the inventors, it has been recognized that when the former area is larger than the latter area, electrolytic reactions no longer occur in both poles when the former electric double layer is not sufficiently formed even though the latter electric double layer is sufficiently formed.
Then, a basic function of increasing the viscosity of the ink using a pH change caused by the electrolysis of the water in the liquid column form is lost, so that even in seeking to improve the ink blur preventability, the stability in ejecting the ink from the nozzle may become difficult. In other words, it is considered that while the above-described technique which increases the contact area is effective to some extent in suppressing reactions in which the ink on the nozzle plate side is prevented from increasing in viscosity, at the same time, it causes reactions in which pH changes in a direction in which the viscosity of the ink is increased on the intermediate transfer body side to be lost.
Thus, the above-described technique which increases the contact area does not become a fundamental solution to a problem of inhibiting the increase in the viscosity of the ink on the intermediate transfer body.
Taking the above into account, it is necessary to avoid the electrolysis at the interface between the nozzle plate and the ink while maintaining electrolytic reactions in both poles and to suppress the pH change towards a direction of preventing the increase in the viscosity of the ink within the head.
Moreover, when the electrolysis occurs at the interface between the nozzle plate and the ink, a problem may arise that the increase in the viscosity of the ink on the intermediate transfer body is inhibited as well as that air bubbles are produced within the head, so that ejecting performance of the ink decreases.
An object of the present invention is to provide an image forming apparatus which provides a recording liquid such as ink, etc., to an intermediate transfer body with a head to perform image forming, wherein the image forming apparatus makes it possible to suppress a change in pH of the recording liquid within the head while utilizing electrolysis of water within the recording liquid to suppress a blur without providing a treatment liquid or a powder other than the recording liquid and which prevents generating of air bubbles within the head by the above-described electrolysis to maintain performance of ejecting the recording liquid from the head.